I used the uTasker project to test this ADC input on the FRDM-KL03Z and didn't have any problems. With debugger connected it disconnects as soon as the port is reconfigured for its analog utilisation, which is as expected, but otherwise (with or without debugger) all works identically and normally.

Attached you can find the binary that you can load to the FRDM-KL03Z.

The output (115200 Baud on the VCOM OpenSDA port) shows the board starting and printing out the ADC value every second:

The crash happens even when the debugger is not attached. I keep seeing prints on UART debug terminal, that are coded before the pin mux setting function call over and over again when running without the debugger.

I used the uTasker project to test this ADC input on the FRDM-KL03Z and didn't have any problems. With debugger connected it disconnects as soon as the port is reconfigured for its analog utilisation, which is as expected, but otherwise (with or without debugger) all works identically and normally.

Attached you can find the binary that you can load to the FRDM-KL03Z.

The output (115200 Baud on the VCOM OpenSDA port) shows the board starting and printing out the ADC value every second: